If the bios screen doesn't flash it's because of your mother board. You had the computer plugged in to a surge protector right? If not, I encourage you to go buy one when/ if we get this up and running.
The hardware you added isn't going to be the problem. If you got your computer up and running and upgraded to Windows 7 (x64.. right?) THEN you were playing on Skype and Steam, it works. I'm sure you looked at the secondary HDD to see if it was working, correct? Please confirm all of this
As far as your computer just not turning on, BUT your PSU and your fans will turn on, please confirm this:
Are the fans plugged straight in to PSU or are the plugged in to the motherboard?
Now, let's see if this will fix the problem. Unplug everything from the motherboard that is coming from the PSU
. You should have a 24 pin connector (or 20+4) a 4 pin connector, and Maybe a 6 pin connector on a graphics card (I'm not looking up your hardware yet.. so there may be more/less)
Now plug it back in
Turn it on and see if it works.
Your hard drives should still be turning on, they are connected straight to the PSU. Even if your computer is not working, your HDDs should be, as well as your CD drive. If they are not, you may have a PSU problem. Steal your boyfriends for a little bit.. "borrow" it
See if it works!